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#4625 ✓resolved

class_inheritable_accessor should let subclasses inherit from the superclass's attribute

Reported by Thomas LECAVELIER | May 17th, 2010 @ 12:31 PM

First a normal case, where things behave as expected:

class A
  class_inheritable_accessor :foo
end = 'foo'

class B < A
end # => 'foo', as expected

Now, a rather disturbing scenario:

class A
  class_inheritable_accessor :foo

class B < A
end = 'foo' # => nil, 'foo' expected

Should we consider that a bug?

Comments and changes to this ticket

  • Neeraj Singh

    Neeraj Singh May 17th, 2010 @ 03:33 PM

    • Tag set to activesupport, patch, rails3

    This is expected behavior. I found following test.

      def test_inheritance
        @klass.class_inheritable_accessor :a
        @klass.a = 'a'
        @sub = eval("class FlogMe < @klass; end; FlogMe")
        @klass.class_inheritable_accessor :b
        assert_respond_to @sub, :a
        assert_respond_to @sub, :b
        assert_equal @klass.a, @sub.a
        assert_equal @klass.b, @sub.b
        assert_equal 'a', @sub.a
        assert_nil @sub.b
        @klass.b = 'b'
        assert_not_equal @klass.b, @sub.b
        assert_equal 'b', @klass.b
        assert_nil @sub.b
        @sub.a = 'A'
        assert_not_equal @klass.a, @sub.a
        assert_equal 'a', @klass.a
        assert_equal 'A', @sub.a
        @sub.b = 'B'
        assert_not_equal @klass.b, @sub.b
        assert_equal 'b', @klass.b
        assert_equal 'B', @sub.b

    As you can see

    @klass.b = 'b'
    assert_not_equal @klass.b, @sub.b

    I am adding two lines to the doc to make it clear that child copies attributes from parents when subclass is created.

  • Neeraj Singh

    Neeraj Singh May 19th, 2010 @ 06:31 AM

    This ticket can be closed. I have update the doc.

  • Rizwan Reza

    Rizwan Reza May 19th, 2010 @ 12:19 PM

    • no changes were found...
  • Rizwan Reza

    Rizwan Reza May 19th, 2010 @ 12:28 PM

    • State changed from “new” to “resolved”

    Thomas LECAVELIER May 31st, 2010 @ 09:57 AM

    • Assigned user set to “Rizwan Reza”

    Thanks for your documentation update. It states very clearly the implementation rationale.

    However, I believe that implementation violates the Principle of Least Surprise, and that the behavior, despite being documented and tested, is not expected.

    What do you think?

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